When properly treated, biological specimens including human tissue and cell lines may be viably stored almost indefinitely at temperatures approaching that of liquid nitrogen, so long as that temperature is maintained. As long as a specimen is stored in a bulk storage facility it is relatively easy to maintain that specimen at a steady liquid nitrogen temperature. However, once the temperature of a specimen is raised significantly, the integrity of the specimen suffers. More specifically, unintended (upward) temperature excursions (UTE's), even falling far short of thawing, may permit the growth of ice crystals inside stored biological samples. Ice crystals may disrupt cell membranes, destroy cellular organelles and genetic material, and render the biological samples inviable. Such damage is irreversible and, if not recorded or reported at the time, may go undetected until the samples are deliberately thawed for use, years or possibly decades later.
When it becomes necessary to move or transfer a specimen, the possibility for uncontrolled and unrecorded temperature excursions occurs. The problem is compounded because an operator may not be aware that a removed specimen has undergone an unacceptable temperature excursion, or, inadvertently allowing such an excursion to occur, may not wish to record such an event out of concern for his or her continued employment and the possibly accurate perception that the damage is unlikely to be discovered during his or her tenure, or possibly, lifetime.
For these reasons, any installation undertaking the long-term cryogenic storage of viable tissue samples and cell lines must embody quality control and quality assurance measures, both to render unintended upward temperature excursions of stored material improbable, and to assure end-users of the improbability of such excursions and of the over-all reliability of the storage facility, to which irreplaceable samples may be entrusted. There is a continuing need for improved devices which will assist in maintaining the temperature integrity of biological samples undergoing cryogenic processing, and in particular, during operations which require the temporary removal of individual specimens from a controlled bulk storage facility and exposure to ambient conditions during such transfer, transportation, or other intermediate steps prior to a final deliberate thawing and use. There is yet a further need for methods and devices which will assure the temperature integrity of a multitude of portable individual samples within a bulk storage facility without the necessity of expensive sensing devices or permanent sensor leads affixed to each cell.